Monday, March 13, 2017

The bull Albertonectes is down deep. Sweeping its massive 7 meter long neck - the longest among elasmosaurs and the most neck vertebrae of any tetrapod - back and forth it lights up bedazzling, psychedielic swarms of bioluminescent organisms of the deep scattering layer. Visible for more than a kilometer this banner of deep sea light plays a purpose for the animal. The elasmosaur is banking on the "deep sea burglar alarm" defense mechanism of the numerous and small denizens of the deep to draw in larger animals for the elasmosaur to ambush.

The deep sea burglar alarm is a rather clever solution to predation in the dark vastness of the abyssal ocean. This theory rests upon the premise that for any predator of the ocean, there is often something bigger that is a predator of that animal. So if a prey animal is attacked in the dark depths a potential tactic would be to call in a larger predator to take out the animal attacking me. Hence the fabulous light show.

The bull is at home in the cold, crushing depths of the high Arctic Bear Paw Ocean. Despite the exertions from these provocations the massive elasmosaur - over 11 meters long and at 4 tons the weight of an Indian elephant - still has the capacity to remain under for at least 40 minutes. A deep rich blubbery layer and abundant super oxygen saturated blood provide the necessary equipment for such dives. With the ambient light provided by the bioluminescent organisms and pressure sensor receptors along the snout and the length of the neck the bull is well attuned to this environment despite the enveloping darkness. While matrilineal pods of Albertonectes ply the shallower oceans of the coastline these big males do their foraging in the deep, cool and productive water in order to gain weight and stamina over other males when the mating season begins. In those months the males feed rarely at all.After the bull elasmosaur has litten up an area half the size of a football field it retreats over to the edge of light show, cloaked in darkness, and waits. He does not have to wait long for out of the blackness emerges another topside explorer of these depths. A primitive scromboid fish, itself equipped with advanced thermoregulatory features that allow it to exploit such productive but cold depths, has arrived to investigate the disturbance. At over a meter long the high octane fish - which usually cruises warmer and shallower water during the day in between dives - is usually met with a welcome feast when it investigates such scenes. And here is no exception as it voraciously ram feeds on the various cephalopods, crustaceans, annelids, jellies, and tunicates swarming in the melee. The visual detection of the fish is geared towards near sighted objects, 10 meters below it it does not see or feel the 11 meter long monster of the deep pivoting slowly into strike position. As the fish makes long and straight passes through the light show picking off small organisms the bull Albertonectes recognizes the pattern and anticipates. The fish is faster in the absolute measure of speed but if the elasmosaur can get within 7 meters it has a good chance of snatching it. Noiselessly and effortlessly the massive elasmosaur shifts and hovers into striking distance below the fish. Running along the length of the vertebral column is a channel filled with oils that allow the animal to change its position in the water column like a predatory stealth submarine. When the fish makes a pass hundreds of muscles fire simultaneously along the 7 meter ling neck drawing it upward and lateral to snatch the fish. These muscles, strongest at the base of the neck anchored along the neural spines and transverse processes, move the massive neck with astonishing speed and accuracy against water resistance. The necks purpose sole here to bring a relatively small but toothy mouth into a position to gain purchase. The fish now can sense the movement of a larger animal below it but here the neck of the Albertonectes outperforms the swimming muscles of the fish. A trailing fin of the fish is snagged by two inch long, deeply rooted fangs. As the bulk of the body of the elasmosaur catches up with the course of swimming the neck has set in motion the mouth opens quickly - the gape is amazing for such a small head - to reposition a bite on the gills of the fish. With bulldog like tenacity temporal muscles squeeze tight on the gills of the fish. 400 meters below the surface of a cool, temperate Cretaceous Artic ocean the life of an ancestor to the tuna dies to support the life of a member of the most resilient and long lasting marine tetrapods ever.

Abyssal Fishing by Duane Nash

The plesiosaur machinations are back!!

As speculative as the above scenario is deep sea burglar alarms are a real thing and considering the ubiquity of bioluminscent organisms in todays oceans such defense tactics likely occurred in Mesozoic oceans as well. Plesiosaurs were probably right there to exploit them as the aquatic bad-asses that they were. Furthermore the take home message - that neck could have been used for all sorts of weird and useful tactics - should not be lost on people.

Because I have said it before and I will say it again: the long neck "plesiosauromorph" bauplan; guild; family - whatever qualifier you want to give it - is the longest tenured and most successful marine tetrapod family of all time. Especially if you go back and consider nothosaurs as part of the radiation plesiosauromorphs beat out macro-pliosuars, ichthyosaurs, sea crocodiles, placodonts, mosasaurs, sea turtles, any and all marine mammal/bird radiations in terms of longevity. Plesiosaurs just kept on sailing along flipping a proverbial middle finger (in the form of a long neck) to all those other marine tetrapod newbies as well as to future hominid interpreters all to eager to characterize plesiosaurs as misshapen, slow, downtrodden, backwards, weak, sucked up, ineffective, cumbersome, ecologically limited and forever the proverbial cannon fodder for the more ferocious, aggressive, and dominant mosasaurs, pliosaurs, ichthyosaurs, sea crocodiles etc. etc.

Changes in plesiosaur perception are not unlike the revolution sauropods had to go through in the dinosaur renaissance. Early interpretations of sauropods depicted them as bipedally rearing, vigorous land animals. At least in attitude and countenance, if not anatomy, some of the earliest depictions and workers on plesiosaurs got more right than many more contemporary interpretations.

Far from being lackluster pushovers, these animals were likely highly combative and highly social and most likelycombative as a social unit (like certain family oriented skinks) against perceived threats. You did not want big mama Terminonator mad at you because she probably has 5 other cohorts circling beneath and around you ready to take the fight to ya and bite you in all those sensitive areas'!!

These animals were sea monsters but they also may have had a sensitive side. The vastness, coldness, depth, and horrific indifference of the open ocean is an existential threat that every lineage of marine tetrapod has to face. Stare at the abyss long enough and the abyss stares back.

This daunting evolutionary challenge for slowly reproducing, high metabolism, social and air breathing marine tetrapods is most often met not only with tight and intricate social bonds but with reassuring physical contact. Plesiosaurs may have indeed eerily reminded us of sauropterygian equivalents to the highly evolved social marine mammals we are familiar with today.

ALL RIGHT, ALL RIGHT, ALL RIGHT!! Do I got the base riled up enough? Do I got ya' singing the sauropterygian gospel yet??

An incipient pivot has occurred. First and foremost people are really starting to take to this notion of plesiosaur being a lot more thicker... bring the thickness people. Not just thick layers of blubber and skin but absolutely daunting packages of muscles powering both fore and hind flippers - because the 2x penguin (credit Robert Bakker) - is a thing. And not just thick straps of muscle around the torso but thick necks - especially towards the base - are also getting traction.

Mark Witton recently wrote a piece Plesiosaur Paleoart: thoughts for artists in which he echoes a lot of the same sentiments I have been espousing in past plesiosaur machinations with regards to neck thickness, torso muscles, generally a more robust appearance. Make 'em thick.

credit Henry Sharpe used w/permission

And then pictures like this!! What the hell are those elasmosaurids investigating a potential meal larger than a trout breaking with the dogma of "they ate only small fish". Blashemy!!

What is this? A throwback of plesiosaurs battling eachother, necks flailing out of the water wildly?!? Restrain your skepticism, it could be that the body is supported from below as the animals are sitting on the seafloor?!?

Mauriciosaurus credit Frey et. al. 2017

A quick little shot out to thick bodied Mauriciosaurus being revealed; further work supporting the aristonectine radiation of filter feeding elasmosaurs; a polycotylid breaking the dogma of "obligate piscivore" and chomping on hesperonithinines.

Yep it does seem like we are in a bit of a renaissance as goes plesiosaurs. And I do detect a faint whiff of plesiosaur machination inspiration in some of these newer interpretations. Long gone are the wimpy, clumsy looking, anachronisms of yore replaced by thick, muscular, confident, and awe inspiring sauropterygian aquatic monster-gods!! Rejoice!!

In light of all these new and wonderful discoveries and depictions of plesiosaurs I want to break with one of my own rules and depict a plesiosaur getting chomped on by another marine predator; not by a mosasaur; not by a pliosaur; not by a shark; but by an ichthyosaur!!

Attenborosaurus vs Macro-predatory Temnodontosaurus credit Duane Nash

I commit such travesty because 1) we don't have many images of macro-predatory ichthyosaurs doing dastardly deeds and 2) Attenborosaurus is one bad ass plesiosaur... urmm pliosaur... what is it?

With regards to point 1) on macro-predatory ichthyosaurs:

We don't often talk enough about macro-predatory ichthyosaurs because though was a big chunk of time in the Triassic to early Jurassic where the marine apex predator throne was held by these guys. Perhaps due to the early and persistent comparison between dolphins and ichthyosaurs we have somewhat eschewed the monstrous and apex nature of some of these animals. I suspect that they were on the whole more sharklike in swimming motion, that they didn't "porpoise" through the water, and probably a little more opportunistic and "reptilian" in their feeding strategy than dolphins. It is a shame we don't have any living shark toothed dolphins around as they might offer better analogy...

I also did not ascribe a species name to the tempo but just went with a generalized large macro-predatory design. I depicted one of the temnos gulping down an immature Attenborosaurus in a swallowing feat many might be skeptical of.

Consider these points:

Modern animals - both with kinetic and akinetic skulls - swallow down quite sizeable things to a somewhat astonishing degree. We do tend to think of bone as quite rigid and "fixed" structurally but in the living animal it is wet and always has some capacity to deform - probably more so than we might assume from dried and brittle skeletal remains.

Ichthyosaurs, possibly due to their "dolphin" like assumed ecology, have been interpreted to have extremely stiff, unyielding dolphin like skulls or even quasi beaks. But look closely at the lower jaw i.e. mandible of ichthyosaurs - the two halves of the jaw, the dentary bones, do not form a solid connecting structure at the tip of the jaw. Unlike the mandibles of dolphins there is no mandibular symphisis.

T. platyodon no mandibular symphysis

Lyme Regis Ichthyosaur credit BNPS no mandibular symphysis

Could elastic tissue there allowed a certain amount of bowing of the lower jaw there to accommodate large parcels of food? Perhaps augmented by some amount of give along the length of jaw and at the jaw hinge? Even just a little flexure would have assisted swallowing large parcels of food… Additionally how rigid is the mandibular connection to the cranium? Could this have bowed out a bit? I don't know - not an expert - but I think there is enough there to ask: why not? Has adherence to ascribing dolphin like affinities to ichthyosaurs inhibited a more thorough investigation of their ecology and feeding apparatus?

In case you have trouble wrapping your head around macro ichthyosaurs there is the pic above. I saw it on Facebook and thought that it needed wider exposure so I can't claim ownership or even permission to use it but in the spirit of spreading the word about these animals you will not find a better visual representation. T. platyodon may have been more of sperm whale than a killer whale, an idea we will revisit shortly. T. eurycehalus, though smaller, offers a more convincing glimpse at the skull of an apex predator ichthyosaur:

T. eurycephalus. credit Ghedoghedo. CC3.0

In addition to Temnodontosaurus and the various "species" that encompass that genus there was; Thalattoarchon saurophagis revealed a few years back; the mysterious, but potentially gigantic, Himalayasaurus; at the 2016 SVP meeting in Salt Lake City, Utah another massive macro-predatory ichthyosaur was announced hailing from British Columbia.

What is very interesting is that these top dog ichthyosaurs all seem to stem from the Triassic and early Jurassic and then they just peter out and disappear into the Jurassic. And this is a trend that seems to have parallel in many lineages of marine tetrapods that achieve apex predator status. An initial burst of diverse forms and then, over time, they wane off into... very often a niche of specialized deep sea teuthophagy (deep sea squid eaters). This is exactly the case with the formerly dominant and massive raptorial sperms whales as they are now represented solely by a dedicated deep sea squid eater. Could it be that many of the latter pliosaurids were actually specialized deep diving teuthophages? Always assumed to represent traditional pliosaur apex predator roles perhaps species such as Brachauchensislucasi; Megacephalosaurus eulerti; Stenorynchosaurus; many of the other quasi polycotylid looking pliosaurs actually had more in common ecologically with sperm whales and pilot whales than killer whales.

Blasphemy right? Suggesting that not all pliosauromorphs were marine apex predators ready to go ape shit on any prey in sight… that some may have been more like sperm or pilot whales?

A constant theme of this blog has been unpacking the cultural baggage that comes along with analyzing extinct animals that are in fact cultural creations. What do I mean when I say that extinct animals that absolutely existed are in fact simultaneously real and cultural creations? The term pliosaur is a loaded terms just as Tyrannosaurus or Smilodon are. When we think of a pliosaur we imagine a huge apex predator that smashed through lesser marine reptiles not necessarily a deep diving specialist on cephalopods… which many later pliosaurs may have been relegated to as sharks and mosasaurs crept into apex predator roles.

Megacephalosaurus eulerti credit MCDinosaurhunter CC3.0

I am not implying that titans like Pliosaurus necessarily evolved into more teuthophagous forms but that over time the apex predators got winnowed away leaving behind deep sea diving squid eating specialists. Life at the top of the photosynthetic marine food web was harsh and any disruption to the system potentially catastrophic for apex predators. However deep sea based food webs - dependent on detritus i.e. "marine snow" and/or chemosynthesis i.e. sulphur consuming organisms, tube worms etc etc. - may offer more stability than shallow water based marine webs dependent on photosynthesis. Which fits the pattern of diverse ichthyosaurs - including macro predator types - getting winnowed away leaving pelagic forms behind; raptorial sperms whales declining in diversity until just a single common teuthophage remains; macro-predatory pliosaurs getting diminished to teuthophagists. Extinct members of the walrus family were once a lot more diverse and some may have been highly predatory - now we are left with an arctic specialist of shelled mollusks. Shark toothed dolphins may have been much more broad in their ecology than most modern dolphins. I would not be surprised if a more predatory extinct penguin comes to see the light of day, if it has not already and we simply have overlooked it…

By the way I thought I would give some exposure to a rather excellent and thoroughly interesting Royal Tyrell Musuem video on the underreported swell of large apex sharks in Cretaceous with some interesting musings on which sharks might emerge as apex marine predators of future oceans.

What should become clear from the above video is how - when an oceanic apex predator declines - another group is waiting in the wings to fill that vacated niche. Nature abhors a vacuum.

So to summarize my thoughts on the matter and to paint with a very broad stroke I detect some common trends in several marine tetrapod adaptive radiations and extinctions:

1) Following large extinction event marine tetrapod clade diversifies rapidly including apex predator and deep sea diving forms.2) Repeated environmental catastrophes usher in extinction events especially at the apex predator role. Deep sea teuthophage specialists remain relatively steady.3) Invasions from other marine tetrapods into vacated marine eco-space inhibit reoccupation of niche space further winnowing away diversity. The last holdouts of formerly diverse radiations occupy offshore, deep diving, teuthophagist niches.4) Large enough perturbations eventually kill off even offshore deep diving specialists rendering a full scale extinction of clade (i.e. ichthyosaurs, marine crocodiles, pliosauromorphs). Animals become so rare that loss of genetic diversity makes extinction a statistical eventuality.
Which brings us right back to the long necked plesiosaurs i.e. the "plesiosauromorph" bauplan. It just kept sailing along. While all of the other marine reptile clades fell away the plesiosauromorph dynasty just kept chugging along, a remarkably consistent pedigree of success.

We have to ask why?

I want to give that question room to breath a bit, I will come back to it in a future post. My current thinking is that plesiosauromorphs were exceptionally opportunistic not just in feeding but in habitat choice. The wide feeding envelop including everything from benthic organisms (clams, worms, crustaceans etc etc), mesopelagic fish/cephalopods, small/weak marine tetrapods, and scavenging combined with an exploitation of marine ecosystems ranging from deep abyssal offshore pelagic (as supported by histological evidence of "the bends") to estuarine/large river complexes offered strong resilience to environmental catastrophes.

And now finally on to point #2) Attenborousaurus is one bad plesiosaur or… pliosaur… what the hell is it anyways?

First things first how cool is it that this animal is named after Sir Richard Attenborough by none other than Dr. Robert Bakker. Back to the gist of the matter is Attenborousaurus a pliosaur or a plesiosaur? Well let us give it the 5th grade test. The 5th grade test is: "does this animal look like the Loch Ness monster?". The answer is unequivocally YES!! Phylogentically this animal is on the path towards latter true macro-pliosaurs that do fit our popular image of what a classic pliosaur does but - sheesh look at the neck - it probably has more in common ecologically and behaviorally with true long necked "plesiosauromorphs". A shape shifter caught in the act of shape shifting.

Yes, it is true that relative to other plesiosauromorphs this animal has a largish head. But in absolute size the head of this animal is not larger than many of the latter elasmosaurids and probably both were capable of the same predatory feats. In essence those that are ok with ascribing mesopredator tendencies to Attenborosaurus should ascribe the same tendencies to other plesiosauromorphs with similar sized jaws. An 18 inch skull with 2 inch teeth is just as effective on a 15 foot animal as it is on a 30 foot animal.

Attenborousaurus credit Adam Smith plesiosaur directory

What we see in Attenborousaurus is a trend towards the apex predator realm, essentially falling short due to the arch predator ichthyosaurs which still occurred in the Sinemarian. The shape shifting plesiosaurs would not be held back and that trend would continue into Rhomaleousaurus a truly impressive animal and perhaps our first best evidence of plesiosaurs making headway into apex predator territory.

Something appears to have opened up the doors for sauropterygians to truly reach this potential. Let us look at a little time line here. Rhomaleosaurus dates to the Toarcian of the early Jurassic. Temnodontosaurus - the complex genus potentially representing the last of the macro-predatory ichthyosaurs - dates from the Hattengian to the Toarcian. Atennborosaurus occurs smack dab in the middle of apex predator ichthyosaur dominion, explaining why it did not become a truly pliosaur looking pliosaur. Could the waning macro-ichthyosaurs - perhaps already trending into deep diving offshore cephalopod specialists with some species of Temnodontosaurs - have allowed the proliferation of true macro-predatory pliosaurs? The suggestion is certainly there…

Or that is what I thought. Further investigation revealed that the daunting panappoly of late Triassic/Early Jurassic plesiosaurs revealed one early macro predatory pliosaur from the Hettangian age of the earliest Jurassic - what has formerly been referred to as "Rhomaleosaurus" megacephalus but which Adam Smith has cleaned up taxonomically as Atychodracon megacephalus. Things always tend to get more complicated the more that you peer into them. I still think that there was an interesting give and take between macro-predatory ichthyosaurs and the first macro-predatory pliosauromorphs. Perhaps the transition was already underway in the late Triassic?

Way back in the Triassic ichthyosaurs and nothosaurs were seemingly in a dead heat for that position as both scary huge Nothosaurus giganteus & N. zhangioccurred and coincided with macro-predaotry ichthyosaurs Thalattoarchon & Cymbospondylus. The ichthyosaurs appear to have won out, I don't know of any macro-predatory nothosaurs making it into the Jurassic. However sauropoterygian relatives of this vanquished class would eventually muscle in over the ichthyosaurs at the apex predator realm.

mandibular symphysis Nothosaurus zhangi credit Liu et al. 2014

Well I'm gonna leave it off right there. Probably a lot to think about; marine arch-predator musical chairs; shape shifting plesiosaurs; the consistent plesiosauromorph bauplan. I hope you enjoyed this and I hope you start to look at plesiosaurs with a new eye. I want to do one more post in the series, end it at lucky number 13 of course, and for this one I want to break one of my own rules: let me know if there are any topics or species I should cover for my last and final installment in the plesiosaur machinations and I will try to work them in. So I am taking requests in the comments.

best,

Duane

Some might be new to the plesiosaur machinations - allow me to indoctrinate. Or, if you have perused the evil machinations before, here is a quick summary and chance to review.

In the introductory post I discuss how a group foraging strategy would facilitate successful and efficient foraging for plesiosauromorphs; make the comparison between white pelicans and grey reef sharks; discussion on a wider prey envelope than generally appreciated; the shark genus Somniosus as a model for cryptic stealth technique.

In this post I advocate the familial unit as the basis for understanding plesiosaur ecology and behavior. I advocate several social lizards - especially skinks - as model organisms for how reptilian aptitude animals can establish social unity and cohesion. Anti-predator behavior is advocated to be antagonist and mobbing cooperative advancements against potential threats.

Embellishing the social unity concept and exploring how simple biochemical feedback loops could have enhanced social unity merely through proximate physical contact. The long neck is proposed as an effective tactile appendage for physical contact.

Plesiosaurs and the misfits. Why you don't want to get bit by a plesiosaur. How many plesiosaurs fall outside the "obligate piscivore" morphology. Occitanosaurus being naughty. Mesopredator plesiosaurs.

Hey babehunter1324 thanks for comments. yes i know of that specimen very interesting. As so often is the case, things get more complex the more we peer deeper. I'll have to peer more into late surviving macro-predatory ichthyosaurs. I don't know if I am completely on board although I could envision some of these late surviving types acting like oceanic white tip sharks, eating you know, like whatever they can in the open ocean. This would be consistent with the baby sea turtle and bird remains. A cosmopolitan deep sea scavenging/opportunist would also be a very resilient niche in the face of environmental catastrophes. Or they could be nearshore opportunists... Will investigate further, thanks!!

Do we know that these last ichthyosaurs specifically descended from teuthophage specialists? Or maybe ichthyosaurs were a lot more opportunistic than generally imagined? Note that I did question this premise in the post...

Whatever the case I do note this pattern of formerly diverse marine tetrapods getting winnowed away to one or two existing types is very common. Sometimes they forage on deep sea squid; sometimes, like walrus, they are benthic grazers; but I think there is a connections between the stability of the ecosystem and its resilience during environmental catastrophes and the resilience of the eco-morphotype.

@Bk Jeong I think people are misinterpreting me. I don't think that ichthyosaurs - or really any marine apex predator "lose out" due to direct competition. More so environmental catastrophes occur, the population gets to low to continue as a species and there is always marine "newbies" that are somehow able to quickly come on the scene and reoccupy the vacated niche. This pattern seems to occur again and again; pliosaurs replacing macro-ichthyosaurs; lamnid sharks replacing pliosuars; mosasaurs replacing lamnid sharks; orcas replacing giant sharks/raptorial sperm whales. Something bad happens to group A, group B fills the slot before any members of group A still surviving can reoccupy that niche.

Lamnid sharks were getting caned into mesopredatory niches throught the Campanian and Maastritchian by Mosasaurs. The largets known species were mako shark sized while Mosasaurs were getting to weights of roughly 10 tons,

Earlier Platypterigius species seem to had been much less specialized towards a tetrapod predation though I had no idea about how smooth that transition was. Maybe Platypterigius will turn out to be paraphyletic. No idea.

Right, I did now just go back and re-read some of the Tet-Zoo Cretaceous Ichthyosuar revolution stuff. It appears that they were doing ok until something happened at the end of the Cenomanian. Why then did plesiosaurs persist? Was it because they found refuge in estuaries/freshwater lakes etc. etc. that ichthyosaurs did not (presumably) occur in?

Cretoxhyrina became extinct at the end of the Santonian. That's leaves over 15 million years in which Mosasaurs were the dominant marine predators, with the largest sharks of the time period being similar in size to the mako shark as I mentioned before. During the Campanian it was mostly Tylosaurids but in the Maastritchian Mosasaurines took over the Northern Hemisphere.

To put into perspective that period of time was roughly five times longer than the difference in time between the latest reliably dated large raptorial Physteroid (Beauamaris teeth) and the known record of Carcharocles (actually Otodus) megalodon. And yet you counted that tiny badly recorded period of time during the Pliocene but not the entire Campanian and Maastritchian.

Yeah Cretoxyhrina may had make it to the Campanian... Only to became extinct roughly one million year latter. That's like saying that Helicoprion was the top predator of the early Triassic in spite of the fact that it became extint roughly one million year after the Permian-Triassic boundary.

As for the second comment I can't just take it seriously. You see, comparing the ammount of fossil teaths of sharks with those of cetaceans is quite pointless because sharks don't stop replacing their teeth throught their life while Cetaceans only do it once. Let's turn the tables. Do you think Otodus megalodon centra are any more common in the Pliocene than raptorial delphinids and physteroids vertebra? Do you think that all those often isoleted bones and teeth of raptorial Physteroids can be dated correctly?

I also hope that your aware that comparassion of the relative ammount of teeth found showed that Otodus megalodon was in decline throught the whole Pliocene, it was just as much of a dead clade as raptorial physteroids.

The other line of lamnids (the line with makos and great whites) however, definitely weren't dead clades swimming. Hell they are still dominant today in spite of the fact larger predators (orcas) exist

It's good to see more 'fat' plesiosaurs coming out in paleoart.Do you have an opinion on what the ingested stones found in Thalassomedon could have been used for? I somewhat doubt that it was used in digestion, since those are used more commonly in herbivorous animals or creatures which have a particularly tough diet.

Hi Beetle Boy, thanks for compliments and comments. With regards to the stones found not just in Thalassomedon but in many plesiosaurs I will delve into that more in my next and final post. Several plesiosaurs show evidence of consuming shelled mollusks (ammonites. clams) so gastroliths may have actually been a potential purpose for them. Note that by putting the crunching/chewing apparatus in the torso weight (in the form of heavy jaw muscles, crunching teeth) can be economized in the head. But I am generally a big fan of feature serviing multiple purposes and I will explore further how such gastroliths may have helped with buoyancy control in the next post...